[container.alloc.reqmts] Fix incorrect change of \mandates to \expects

This was incorrectly changed from a \mandates to an \expects when
93ff092 replaced the requirements
tables.

Author: jwakely

source/containers.tex

@@ -1031,7 +1031,7 @@
 \tcode{A}
 
 \pnum
-\expects
+\mandates
 \tcode{allocator_type::value_type} is the same as \tcode{X::value_type}.
 \end{itemdescr}